The skin is the largest and most exposed organ of the body. its functions are complex and include serving as a physical and immunologic barrier to external substances, retaining water, regulating body temperature, and acting as a sensory organ. The skin is also an integral part of our self-image and is often a focus of cosmetic and beautifying agents.
The skin consists of three layers. The upper layer, or epidermis, is about as thick as a sheet of paper. It is composed of layered skin cells called keratinocytes. The outermost part of the epidermis, called the stratum corneum, is composed of dead keratinocytes that are shed continuously. The living layer of keratinocytes underneath is called squamous cells. The innermost part of the epidermis consists of basal cells that are constantly dividing to form new keratinocytes. The bottom skin layer is called the dermis, which contains tiny blood and lymph vessels that increase in number deeper in the skin. Cells called melanocytes form the transitional layer between the epidermis and dermis. These skin cells produce a brown-black skin pigment called melanin, which helps to protect against the damaging rays of the sun and also determines skin coloring. As a person ages, melanocytes often proliferate, forming concentrated clusters that appear on the surface as small, dark, flat, or dome-shaped spots, which are usually harmless moles or liver spots.
Because the skin is exposed to the environment, it is susceptible to damage over time. Ultraviolet rays from sunlight and smoking are the most common causes of environmental skin damage. Sunlight consists of ultraviolet (referred to as UVA or UVB) radiation that penetrates the layers of the skin. UVB radiation primarily affects the outer skin layers and is the primary cause of sunburn. it affects skin cells by damaging the genetic material, the DNA, inside the skin cells. UVA radiation penetrates into the inner skin layers and is responsible for tanning and allergic reactions to sunlight (such as from medication). UVA causes the release of oxidants, or oxygen free radicals, that can damage cell membranes and interact with genetic material. Cigarette smoke also produces oxygen free radicals and is known to accelerate wrinkles and aging skin disorders.
Sun protection is one of the most important parts of a skin care regimen. Research has shown that exposure to UV light can cause various skin cancers, the most common being basal cell carcinoma and squa-mous cell carcinoma. A less common but much more dangerous form of skin cancer, malignant melanoma, may be linked to sunburns in childhood.
UVA and UVB radiations cause dramatically accelerated skin aging, including wrinkling, dryness, visible blood vessels, and changes in pigmentation. Sunlight damages collagen fibers (the major structural protein in the skin) and causes accumulation of abnormal elastin (the protein that causes tissue to stretch). Large amounts of enzymes called metalloproteinases are produced in response to the abnormal elastin that function to remodel the damaged tissue by manufacturing and reforming collagen. In addition to sun damage, smokers have considerably higher levels of these metallo-proteinases, which may contribute to the skin-aging effects of smoking. Unfortunately, the reformation process is imperfect and some metalloproteinases actually degrade collagen. The result is an uneven formation of disorganized collagen fibers called solarscars. Repetition of this imperfect skin rebuilding over time causes wrinkles.
Healthy skin care and habits can decrease this cumulative injury. Recommendations include:
- Minimizing sun exposure during peak hours (10 AM to 2 pm).
- Wearing sun-protective clothing, hats, and sunglasses.
- Using a broad-spectrum sunscreen (UVA and UVB protection) with a sun-protection factor (SPF) of greater than or equal to 15.
- Avoiding sunlamps and tanning beds.
- Avoid cigarette smoke; if you smoke, quit.
Protective sun exposure habits are most beneficial when started in childhood since statistics show that more than one half of a person’s lifetime UV exposure occurs during childhood and adolescence. However, it is never too late to incorporate sun protection into a skin care regimen. Medical treatments for reversing some of the effects of sun damage are available and include topical creams, chemical peels, and laser therapy.
Other components of a skin care regimen need not be complicated. Mild, nonperfumed soaps are usually recommended for cleansing the skin, with a moisturizer applied as needed (consider products that have a built-in sunscreen). As we get older, our skin has fewer sweat and oil glands and is less efficient in retaining water, which can lead to dryness and itching. Dry skin can be worsened by frequent bathing or showering, and may be more sensitive to soaps, cosmetics, and certain fabrics. Frequent use of emollients and avoiding aggravating factors are basic measures for dry skin care. For those with oily or acne-prone skin, facial moisturizers are usually not needed and care should be taken to choose cosmetics that are oil-free and non-comedogenic (acne-producing).